The use of blood culture media to ascertain the presence and identity of microorganisms in medical and laboratory research applications is well known. In use, the culture medium is inoculated with, for example, a scraping from the environment or patient, incubated, and then studied for the presence of characteristic microbial growth patterns. Typically, such a protocol is carried out in a sterile "clean room." In order for the testing to be accurate, it is absolutely essential that the culture media be totally sterile prior to the test. This is generally accomplished by sterilizing the media immediately prior to the inoculation in an isolation chamber by contacting the packaging of the media with a sterilizing agent at ambient temperatures. Conventional sterilizing agents, used in vaporized mist form, are aqueous solutions of hydrogen peroxide, formaldehyde, peracetic acid, and mixtures thereof.
A major problem associated with the use of such sterilizing agents is that they are sufficiently corrosive to attack and break down and so penetrate the packaging for the culture media, thereby allowing premature exposure of the media to the environment, along with contamination of the media by the sterilizing agent. Attempts have been made to address this problem by enclosing the culture media in heavy gauge packaging material to form a vapor barrier. However, this method in turn often leads to the formation of "wet" culture media due to evaporation of water contained within the media, followed by condensation within the packaging material. The formation of moisture on culture media, even in slight amounts, is problematic in that the characteristic growth patterns of microorganisms tend to become blurred and indistinct, thereby preventing proper identification of the microorganism in question. To allow moisture to escape, semipermeable packaging material such as bonded olefin (sold by DuPont as Tyvek.RTM.) has been used, but this material is insufficiently resistant to attack by the conventional sterilizing agents mentioned above.
Clean rooms are also used for other medical and laboratory research applications, and for fabrication and handling of items that are extremely sensitive to microbial contamination. To maintain such clean rooms and equipment therein in relatively sterile condition, sterile absorbent wipes and sterilizing solutions are routinely used. However, the packaging for such wipes and solutions is itself subject to microbial contamination when it is in storage awaiting use.
There is therefore a need for packaging that is capable of maintaining a sterile item in a sterile and dry condition, while at the same time being capable of withstanding chemical attack by commonly used sterilizing agents. These needs and others are met by the present invention, which is summarized and described in detail below.